POS0431 GOBLET CELL SPECIFIC ANTI-APOPTOTIC ROLE OF INTERLEUKIN-24 IN SPONDYLOARTHRITIS-ASSOCIATED ILEITIS
Authors: A. Cameron, R. Giri, J. Begun, T. Wells, A. S. Bergot, R. Thomas
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Spondyloarthritis (SpA) is characterised by chronic debilitating axial and peripheral joint inflammation, often concomitant with inflammatory bowel disease (IBD)-like gut phenotypes. However, the contribution of extra-articular gut pathologies to SpA is not well understood. The ZAP-70<sup>W163C</sup> BALB/c (SKG) mouse model of SpA develop chronic arthritis, spondylitis and IBD-like ileitis commencing from 1 week after intraperitoneal curdlan injection with characteristic interleukin-23-dependent gut dysbiosis, endoplasmic reticulum (ER) stress and goblet cell depletion. The cytokine interleukin-24 (IL-24) was first described to promote ER stress-mediated apoptosis in damaged tumour cells without harming normal cells. Conversely, IL-24 attenuated cell death in a liver damage model. IL-24 levels were increased in the synovial fluid in SpA and in the colon in IBD. <h3>Objectives</h3> Since, in both IBD and SpA, gut dysbiosis and mucus depletion promote goblet cell stress and apoptosis, we therefore assessed the role of gut derived IL-24 in ER stress-mediated apoptosis in SpA. <h3>Methods</h3> Ileal histology sections from curdlan-treated SKG mice were stained with Alcian blue staining or immunofluorescence (IF) using an anti-IL-24 Ab. The human MUC2<sup>hi</sup> colonic epithelial cell line, LS-174T was compared to the MUC2<sup>low</sup> colonic epithelial line HT-29 after induction of ER stress with SERCA-inhibitor thapsigargin in the presence of IL-24 or control siRNA. Gene expression was analysed by RT-qPCR and protein by Western Blot or flow cytometry. <h3>Results</h3> Naïve SKG ileum displayed dysbiosis with increased expression of ER stress markers <i>Grp78, sXBP1</i>, <i>CHOP</i> and reduced mucin staining. After curdlan treatment, goblet cell numbers were decreased and <i>Il24</i> mRNA was increased compared to BALB/c controls. By IF, IL-24 localized to the goblet cells of the ileum in SKG and BALB/c mice and 2 weeks post curdlan, ileal goblet cell number was correlated with IL-24 staining intensity. In MUC2<sup>hi</sup> LS-174T but not MUC2<sup>low</sup> HT-29 cells, thapsigargin induced a rapid and transient increase in <i>Il24</i> transcription and subsequent ER stress with <i>CHOP</i> induction, suggesting an acute goblet cell-specific response associated with high mucus production. IL-24 knockdown in LS-174T increased ER stress and apoptosis including increased <i>CHOP</i>, <i>DR5</i> and active caspase 3 expression. <h3>Conclusion</h3> Despite goblet cell IL-24 over-expression in dysbiotic naïve SKG ileum, goblet cell loss due to stress associated with increased mucus production also depletes IL-24. In an in vitro model of goblet cell stress, IL-24 mitigates ER stress-induced apoptosis, suggesting that IL-24 production in SKG ileum is insufficient to prevent the disease cascade that commences with goblet cell apoptosis and epithelial barrier breakdown. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.